1. Field of the Invention
The present invention relates to a photoconductor used for electrophotographs, electrostatic recording, electrostatic printing and the like, a photoconductor cartridge in which the photoconductor is incorporated, and an image-forming apparatus in which the photoconductor is incorporated.
2. Description of the Related Art
An electrophotographic method using a liquid developing agent has advantages of realizing a high resolution image quality by using a fine toner of sub-micron size, acquiring a sufficient image density with a small amount of toner, and the like. These advantages cannot be realized by an electrographic method using powder toner.
The photoconductor of an image-forming apparatus using a liquid developing agent has a structure in which a photoconductive layer is formed on a conductive substrate. The photoconductive layer is formed from organic materials, inorganic materials or amorphous silicon (a-Si) materials. The photoconductive layer formed from an a-Si material has a high hardness and therefore the photoconductor having the photoconductive layer (a-Si photoconductor) has a high wear resistance. However, when developing is performed using an a-Si photoconductor under a high humidity condition, there occur image deletions. Thus, in order to improve the hydrophobicity of an a-Si photoconductor to prevent image deletions, there was discussed a coating of the surface of a photoconductive layer formed from an a-Si material with a surface protection layer comprising fluorine-containing amorphous silicon carbide or fluorine-containing amorphous carbon, the coating described, for example, in Patent Document 1 (JP-A-2001-13703). There was also discussed a coating of the surface of a photoconductive layer formed from an a-Si material with a surface protection layer containing a thermosetting fluorine-containing polyimide as a major ingredient, the coating described, for example, in Patent Document 2 (JP-A-5-119502). When dry developing is performed using the a-Si photoconductor on which a surface protection layer is provided, discharge products adhere to the surface protection layer to cause image deletions. When wet developing is performed using the a-Si photoconductor on which a surface protection layer is provided, a liquid developing agent adheres to an undeveloped area of the surface protection layer, leading to photographic fog.
In order to prevent a liquid developing agent from adhering to the undeveloped area of the photoconductor, there was discussed a coating of the surface of an a-Si photoconductor with a release layer comprising an amorphous fluorine resin, the coating described, for example, in Patent Document 3 (JP-A-2002-278121). The release layer has a thickness of less than or equal to 10 nm, and therefore, as printing by means of an image-forming apparatus in which the photoconductor is mounted proceeds, oil repellency coming from an amorphous fluorine resin ceases to be exerted, thereby reducing the contact angle of a liquid developing agent on the photoconductor. That is, it is difficult to maintain the function of the photoconductor for a long time.
On the other hand, the hardness of a photoconductive layer formed from an organic material and a photoconductive layer formed from an in organic material is low, and therefore, the wear resistance of photoconductors having these photoconductive layers is not high. The photoconductor (organic photoconductor) having a photoconductive layer formed from an organic material has such a short lifetime as several to six months and the extension of the lifetime of an organic photoconductor is a problem to be solved. Further, there are also problems that carrier liquid adheres to the non-image area of the organic photoconductor, thereby causing scumming and image deletions or that the amount of cleaning toner is not reduced, making the control of the concentration of a liquid developing agent difficult. These problems are also to be solved.
Therefore, there was discussed a combination of an organic photoconductor on which a surface protection layer containing a fluorine resin is formed with a wet developing agent using isoper, silicon oil or the like as a carrier liquid, the combination described, for example, in Patent Document 4 (JP-A-5-40357) and in Patent Document 5 (JP-A-2002-278121). Further, there were also discussed an organic photoconductor having a contact angle (θ) of a solvent such as isoper or the like to the surface protection layer of 20°<θ<110°, having a good toner transferability and causing no image deletions, the photoconductor described, for example, in Patent Document 6 (JP-A-2000-267447) and an organic photoconductor having a contact angle (θ) to a surface protection layer containing a fluorine resin of more than or equal to 30° and having high transferability and cleanability, the photoconductor described, for example, in Patent Document 7 (JP-A-2002-351155). There was also discussed an organic photoconductor on which a surface protection layer containing fluorinated organopolysiloxane, the photoconductor described, for example, in Patent Document 8 (JP-A-10-288872). The organic photoconductor on the surface of which a solution containing a resin dissolved in a solvent is applied and a resin-containing surface protection layer is formed has a low coating strength, and as is clear from the comparative examples described later, when a cleaning test is repeated as a load test, there occurs a problem that the contact angle on the surface protection layer is reduced, resulting in a lowered water- and oil-repellency performance. Further, the use of a perfluoro solvent applied on the fluorine resin is regulated in view of global warming.